Gas turbine jet propulsion engine igniter



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United States Patent 3,264,825 GAS TURBINE JET PROPULSION ENGINE IGNITERGordon Allan Halls and Leslie Barnes, both of Littleover, Derby,England, assignors t0 Rolls-Royce Limited, Derby, England, a Britishcompany Filed Sept. 1, 1965, Ser. No. 491,476 6 Claims. (Cl. 6039.82)

This invention concerns a gas turbine jet propulsion engine combustionchamber and is a continuation-in-part of our application Serial No.183,907, filed Mar. 30, 1962, now abandoned.

A problem associated with all internal combustion engines usingelectrical ignition systems is that of ensuring continuity of operationeven after failure of a component of the system. This problem isparticularly serious in gas turbine jet propulsion engines since failurein operation could result in loss of life and/or loss of an expensiveaircraft.

It is clear that the problem can be overcome by duplicating the ignitionsystem. Thus, if a 12 joule igniter is required to relight an engineshould flame out occur at 40,000 feet, then two 12 joule igniters andassociated circuits could be employed to ensure increased safety.However, the obvious penalty of the solution is an increase in weight of100% in the ignition system.

To reduce this penalty, We propose to replace a single 12 joule ignitionsystem with two 6 joule ignition systems. By arranging the surfacedischarge igniters of two 6 joule systems such that their dischargecombine, it has been found that an ignition equivalent to or even betterthan that produced by a single 12 joule system is obtained. Thus relightat, say, 40,000 feet is possible. Should one of the igniters or systemsfail, relight can be obtained by dropping to, say 30,000 feet, when theremaining igniter would be capable of relighting the engine. Thu aneffectively duplicated system is provided, the weight increase of whichis only 8% compared with a single 12 joule system. Although some loss inheight may be necessary to effect ignition with the remaining igniter,this is obviously preferable to being without an additional igniter orhaving a weight penalty of 100%.

It will be appreciated that the system herein proposed may be ofparticular use at take-off or on an approach run when, if flame outshould occur and one igniter should fail, the remaining 6 joule ignitercan be used to relight. If a single 12 joule igniter is used, no relightwould be possible, and if two 12 joule igniters are used the weightpenalty is excessive.

In employing two 6 joule igniters to provide ignition similar to orbetter than a single 12 joule igniter, it is important to ensure thatthe combustion zones produced by the igniters combine to provide theequivalent of a 12 joule combustion zone since otherwise performancewill be no better than with a single igniter. It will be seen that theconsideration here is totally different from that used in employing twoigniters in a piston engine, for example, where, to obtain a rapid flamepropagation in the combustion chamber, two igniters may be placedtherein, as far apart as possible.

According, therefore, to the present invention, a combustion chamber, ina gas turbine jet propulsion engine,

3 ,264,825 Patented August 9, 1966 has two surface discharge sparkigniters which individually could not produce light-up at apredetermined altitude, and means for simultaneously firing the twospark igniters to produce combustion zones which combine and can producelight-up at said predetermined altitude, said means being capable offiring the spark igniters individually to produce light-up at altitudesless than said predetermined altitude.

Each of the spark igniters may be connected to a separate source ofelectrical energy, the two sources of electrical energy being soarranged that the spark igniters are fired simultaneously orsubstantially simultaneously.

In this case each said source may be connected to its spark igniter by acircuit which is electrically or magnetically coupled to the othercircuit. Thus each said circuit may comprise a sealed spark gap having atrigger electrode which is triggered by the passage of current in theother circuit.

Alternatively, and preferably, the two spark igniters may be connectedin series across a single source of electrical energy.

The or each said source of electrical energy may be substantially of thevalue six joules.

The invention is illustrated, merely by way of example in theaccompanying drawings, in which:

FIGURE 1 is an axial section through part of a combustion chamberaccording to the present invention, the said combustion chamber formingpart of a gas turbine engine and being provided with a pair of sparkigniters,

FIGURES 2 and 3 are schematic cross sections illustrating alternativeelectric circuits in which the spark igniters shown in FIGURE 1 may beconnected, and

FIGURE 4 is a circuit diagram illustrating a circuit which may beemployed to effect substantially simultaneous operation of the sparkigniters shown in FIG- URE 1.

Referring first to FIGURE 1, a gas turbine engine has an engine casing11 and an inner casing 12 (shown in FIGURES 2 and 3) which are separatedby an annular space 13 and which constitute the outer and inner wallsrespectively of the combustion chamber of the engine.

Mounted within the space 13 are a number (e.g. eight, as shown) of flametubes 14 which are angularly spaced apart from each other. Between eachadjacent pair of flame tubes 14 there are interconnecting passages (notshown) through which flame propagation may occur.

Alternatively, instead of providing a number of angularly spaced apartflame tubes, a single fully annular flame tube may be employed.

Air enters each of the flame tubes 14 at 15, fuel being injected intoeach of the flame tubes by means not shown.

One of the flame tubes 14 is provided with a pair of spark igniters 16,17.

The spark igniters 16, 17 are fixed in the casing 11 and extend acrossthe space 13 so that their respective inner ends 20, 21 (which areprovided with spark electrodes, not shown) project through the wall ofthe respective flame tube 14 and into the combustion zone within.

The spark igniter 16, 17 are situated very close together such that onsimultaneous or substantially simultaneous operation of the sparkigniters, the hottest parts of the immediately developed individualcombustion zones produced by the spark igniters are closely adjacent toor meet each other.

It has been found that when the hottest parts of the immediatelydeveloped combustion zones from the spark igniters 16, 17 combine, asuperior ignition performance is obtained to that produced by a singlespark. Moreover even if the spark igniters 16, 17 are energised byseparate six joule sources of electrical energy, the ignitionperformance obtained is substantially equal to that obtained from asingle spark igniter energised by a twelve joule source of electricalenergy.

It will be appreciated that once the spark igniters 16, 17 effectignition within the flame tube 14 within which they are disposed, theprovision of the above-mentioned interconnecting passages will ensurethat ignition also occurs within the remaining flame tubes 14.

Although the spark igniters 16, 17 are shown as being inclined to oneanother, this is not essential and indeed it is preferred that theyshould be parallel to each other.

In FIGURE 4 there is shown a circuit which may be employed to effectsubstantially simultaneous operation of the spark igniters 16, 17 ofFIGURE 1.

The circuit of FIGURE 4 includes two charging sources 26, 27 each ofwhich is connected across a twenty-four volt source of direct current.The charging sources 26, 27 are adapted to chop the direct currentsupply to produce highvoltage pulses of current.

The charging sources 26, 27 are connected, by way of rectifiers 28, 29respectively, and lines 30, 30 respectively, to choke couplings 31, 32respectively. Earthed condensers 33, 34 are arranged to be charged withpulses of current from the rectifiers 28, 29 respectively. Thecondensers 33, 34 when fully charged, each contain six joules of storedenergy.

The choke couplings 31, 32 are connected to the spark igniters 16, 17respectively by way of sealed spark gaps 35, 36 respectively.

The sealed spark gaps 35, 36 are provided with trigger electrodes 37, 38respectively. The trigger electrodes 37, 38 are respectively connectedto the choke couplings 32, 31.

Accordingly, if, for instance, the condenser 33 becomes fully chargedbefore the condenser 34, the sealed spark gap will break down andignition current will pass to the spark igniter 16. The passage ofcurrent through the choke coupling 31 will, however, trigger the sealedspark gap 36 by way of the trigger electrode 38, and ignition currentwill also pass substantially simultaneously to the spark igniter 17.

Thus the spark igniters 16, 17 will always be operated substantiallysimultaneously.

The arrangement shown in FIGURE 4 is only one of several ways in whichthe spark igniters 16, 17 may be operated substantially simultaneously.

Thus the choke couplings 31, 32, instead of being connected to triggerelectrodes '37, 38, may be connected to third electrodes (not shown) inthe sealed spark gaps 36, 35 respectively.

Alternatively the choke couplings 31, 32 may be dispensed with and thelines 30, 30' magnetically coupled together by incorporating chokes (notshown) which are wound on a common core (not shown).

Another possibility is to dispense with the choke couplings 31, 32 andthe two sealed spark gaps 35, 36, and to use instead a single commonsealed spark gap (not shown), whereby the discharge of one condenserwould cause discharge of the other.

It is also possible to couple the lines 30, 30' by transformer couplingor by resistance coupling.

In FIGURE 2, the spark igniters 16, 17 are respectively energised fromseparate, six joule, sources 22, 23 of electrical energy, the sparkigniters 16, 17 being caused to operate simultaneously e.g. by the useof a circuit as shown in FIGURE 4.

In FIGURE 3, each of two diametrically oppositely disposed flame tubes14 is provided with a pair of spark igniters 16, 17. The spark igniters16, 17 of each said pair are wired in a series circuit across a single,six joule, source 24 of electrical energy. The said series circuit mayincorporate a switch (not shown). This system is particularly useful indirect lift engines.

The arrangements described above also have the advantage overconventional gas turbine engine combustion systems that the life of thespark igniters is substantially increased due to the lower electricalenergy used (six joules as opposed to twelve joules).

Thus the double igniter arrangements described above may be used toreplace each of the'single igniters of conventional ignition systems,even if two or more single igniters are used at opposite sides of theannular chamber to promote flame propagation. By replacing each 12 jouleigniter with two adjacent 6 joule igniters, a duplicate ignition systemis provided with a weight penalty of, say, only 8% compared with the tobe expected by using two 12 joule igniters. By employing two six joulesystems, re-light may be effected at, say 40,000 feet, which is as goodas if not better than that provided by a 12 joule igniter. Should one ofthe 6 joule igniters fail, re-light may be obtained by dipping to, say,30,000 feet and operating the remaining igniter alone.

It has been found that the time to light of an engine using thecombustion chamber illustrated in FIGURE 2 or 3 is not substantiallydifferent from the time to light of an engine using the above-mentionedconventional combustion system. Also, the engine is lighter, and due tothe duplicated ignition system, is safer.

We claim:

1. In a gas turbine jet propulsion engine, a combustion chamber havingtwo closely adjacent surface discharge spark igniters which individuallycould not produce lightup at a predetermined altitude, and means forsimultaneously firing the two spark igniters to produce combustion zoneswhich combine and can produce light-up at said predetermined altitude,said means being capable of firing the spark igniters individually toproduce lightup at altitudes less than said predetermined altitude.

2. In a gas turbine jet propulsion engine, a combustion chamber havingtwo separate sources of electrical energy, two closely adjacent surfacedischarge spark igniters, which individually could not produce light-upat a predetermined altitude, connected one to each source, and means forsimultaneously firing the two spark igniters to produce combustion zoneswhich combine and can produce light-up at said predetermined altitude,said means being capable of firing the spark igniters individually toproduce light-up at altitudes less than said predetermined altitude.

3. In a gas turbine jet propulsion engine, a combustion chamber having asingle source of electrical energy, two closely adjacent surfacedischarge spark igniters, which individually could not produce light-upat a predetermined altitude, connected across said single source, andmeans for simultaneously firing the two spark igniters to producecombustion zones which combine and can produce light-up at saidpredetermined altitude, said means being capable of firing the sparkigniters individually to produce light-up at altitudes less than saidpredetermined altitude.

4. In a gas turbine jet propulsion engine, a combustion chamber havingtwo relatively inclined, closely adjacent surface discharge sparkigniters which individually could not produce light-up at apredetermined altitude, and means for simultaneously firing the twospark igniters to produce combustion zones which combine and can producelight-up at said predetermined altitude, said means being capable offiring the spark igniters individually to produce light-up at altitudesless than said predetermined altitude.

5. In a gas turbine jet propulsion engine, a combustion chamber havingtwo electrical circuits, a source of electrical energy and a surfacedischarge spark igniter a sealed spark gap having a trigger electrodewhich is triggered by the passage of current in the other circuit.

6 References Cited by the Examiner UNITED STATES PATENTS 2,025,203 12/1935 Harper 123-148 2,456,475 12/1948 Wargin et a1 315-213 2,590,7783/1952 Lautenb'erger 123148 2,687,184 12/ 1954 Lautenberger.

FOREIGN PATENTS 592,534 1/1925 France.

MARK NEWMAN, Primary Examiner.

R. D. BLAKESLEE, Assistant Examiner.

1. IN A GAS TURBINE JET PROPULSION ENGINE, A COMBUSTION CHAMBER HAVINGTWO CLOSELY ADJACENT SURFACE DISCHARGE SPARK IGNITERS WHICH INDIVIDUALLYCOULD NOT PRODUCE LIGHTUP AT A PREDETERMINED ALTITUDE, AND MEANS FORSIMULTANEOUSLY FIRING THE TWO SPARK IGNITERS TO PRODUCE COMBUSTION ZONESWHICH COMBINE AND CAN PRODUCE LIGHT-UP AT SAID PREDETERMINED ALTITUDE,SAID MEANS BEING CAPABLE OF FIRING THE SPARK IGNITERS INDIVIDUALLY TOPRODUCE LIGHTUP AT ALTITUDES LESS THAN SAID PREDETERMINED ALTITUDE.